Soil sampling tools and devices are used for a variety of purposes, e.g., to obtain samples for soil moisture content or to learn whether and to what extent a volatile organic compound (VOC) may have permeated the soil. And soil cores are removed for other reasons unrelated to VOC analysis. Examples of soil coring and sampling tools are shown in U.S. Pat. No. 3,326,049 (Eley); U.S. Pat. No. 3,444,938 (Ballman); U.S. Pat. No. 3,497,018 (Schultz et al.); U.S. Pat. No. 4,729,437 (Zapico); U.S. Pat. No. 4,819,735 (Puckett); U.S. Pat. No. 4,888,999 (Kozak); U.S. Pat. No. 4,989,678 (Thompson); U.S. Pat. No. 5,505,098 (Turriff et al.); U.S. Pat. No. 5,522,271 (Turriff et al.) and U.S. Pat. No. 5,517,868 (Turriff et al.).
The invention relates particularly to soil sampling for assaying a VOC which may be present in a sample. It is common knowledge that tanks for storing liquid may, over time, develop a leak. If the tank is above ground, the leak is usually observed rather soon after its onset and not much damage results. On the other hand, there is an already-substantial and growing awareness that certain types of liquid storage tanks placed underground have a greater-than-normal propensity to deteriorate and leak. Such types include tanks made of steel from which protective coatings have either been eaten away or were non-existent.
And a substantial factor contributing to the risk of tank leakage is that with an underground tank, leakage is not visible. Usually, such leakage, its seriousness and appropriate remediation steps can only be determined after excavation and testing.
Undetected leaks of underground storage tanks can and do contaminate soil and potable water supplies. Because of the number of gasoline service stations and private fuel and solvent storage tanks, leakage of volatile organic compounds (VOCs) such as petroleum distillates, hydrocarbons, ketones, acetates and the like is a problem of particular concern.
Good remediation requires that personnel be able to accurately determine the nature and extent of the leak. This involves ascertaining the degree to which soil may be contaminated by a VOC. Analysis of VOC contamination of a soil sample is by placing the sample into a laboratory vial with chemicals used for such analysis.
To accurately analyze the type and degree of VOC contamination, it is important that the sample be preserved during transportation from the field site to the laboratory and during any storage of the sample prior to analysis. Good sample preservation requires that the sample be isolated from air so as to yield a sample for post-coring analysis that evidences substantially the same level and type of VOC contamination as prevailed when the sample was first cored from the earth. Good sample preservation becomes more difficult when, as is often the case, analysis occurs significantly later in time than the actual coring.
A recently-identified difficulty relating to sampling tools of the type disclosed in the Turriff et al. patents (i.e., tools having caps for VOC entrapment) is that air can become trapped between the cap and the barrel. Such trapped air may prevent a good seal and has the potential to permit VOC to volatilize to some degree before the soil sample can be analyzed.
The corer disclosed in the Schultz et al. seemingly evidences the same difficulty. And in any event, coring tube closure is by sliding the tube downwardly into a sheath mounted on a shelf of a submersible vessel, a wholly-impractical arrangement for above-ground, field site sampling.
The Schultz et al. corer has another feature which presents a subtle but very-real disadvantage in VOC sampling applications. That corer has a small but discernible "dead volume" trapped at the stopper. Air dead volume in a VOC sampling tool is disadvantageous because such trapped air provides a medium into which VOC may migrate and impair the integrity of the sample.
Still another disadvantage of the Schultz et al. corer in VOC applications is that such corer is for use with saturated soil, i.e., soil at the bottom of a lake. Typical VOC sampling tools are used for soil sampling in the vadose zone, i.e., the zone of soil between earth surface and the water table. Typically (although not absolutely), the water content of such soil in the vadose zone will be in the range of 20% or below.
Yet another disadvantage of sampling tools such as that disclosed in the Turriff et al. '771 patent is that the cover is secured to the barrel only by friction. A cover which inadvertently falls from the barrel during transportation and/or storage is likely to make the sample unreliable.
An improved sampling tool and method which address disadvantages inherent in prior art sampling tools would be a significant advance in this technical field.